1. Field
The present disclosure relates generally to navigation systems and in particular to navigation systems that use global positioning systems and inertial measurement units. Still more particularly, the present disclosure relates to a low authority global positioning system aided inertial navigation system with anti-GPS-spoofing for use on moving vehicles.
2. Background
A global positioning system (GPS) is a space based radio navigation system that provides reliable positioning, navigation, and timing services on a continuous world-wide basis. A global positioning system includes satellites orbiting the earth, control monitoring stations on the earth, and global positioning system receivers. The global positioning satellites broadcast signals from space that are received and tracked by global positioning receivers. Each global positioning receiver may then estimate and provide a three dimensional location. This three dimensional location may include, for example, latitude, longitude, and altitude. Additionally, time may be obtained from these signals that are broadcast by the satellites.
Global positioning systems have been employed in many navigation applications. Some concerns exist in using global positioning system information in some types of navigation systems. These concerns are present when certain levels of accuracy of the location of the vehicle are absolutely needed. In some cases, global positioning system performance may degrade in environments in which jamming, interference, or radiation is present. These types of situations are of concern for both military and commercial aviation applications. However, when global positioning system accuracy degrades, this degradation is usually detected by the integrity-monitoring flight software. Further, various measures are available to counter these types of problems.
In some cases, spoofing of global positioning signals also may occur. In other cases, meaconing of the signals also may occur. Meaconing involves the interception and rebroadcast of navigation signals. These signals may be rebroadcast on a received frequency to confuse adversarial global positioning system navigation systems. As a result, an aircraft may compute an inaccurate location.
With respect to spoofing and meaconing of global positioning signals, the accuracy may be severely degraded beyond a desired range. These types of global positioning system threats and anomalies are more difficult to detect.
Therefore, it would be advantageous to have a method and apparatus for a navigation system that overcomes these problems.